The invention is directed to a method for optimisation of transmission links in a cellular telecommunications network.
FIG. 1 shows an example of a situation which sometimes occur during a hard handover, i.e. when a mobile station 10 changes the base station or base stations 20 it uses. Such a situation may occur, for example, when a mobile station moves from one cells to another in a cellular telecommunication system. FIG. 1 depicts two situations, situation A, when the mobile station 10 is still in the area of the first cell, and situation B, when the mobile station (MS) has moved to the area of the second cell. FIG. 1 shows also base stations (BS) 20, which are controlled by radio network controllers (RNC) 30, 31. The radio network controllers are connected to a mobile switching center (MSC) 40. In the first situation, the mobile station 10 is in position marked by the letter A, having connections to base stations 20 controlled by the first RNC 30. The radio network controller 30 comprises combining 33 and splitting 34 units. Combining units 33 combine uplink signals belonging to the same bearer coming from different base stations, and splitting units replicate downlink signals to more than one base station. The RNC 30 also comprises a protocol control block 32, which executes the protocols needed for communication with the mobile station 10. The RNC 30 forwards the uplink data to, and receives downlink data from, the MSC 40, which communicates with the rest of the telecommunications network.
When the mobile station moves to the position marked by the letter B, the mobile station 10 establishes radio links to the base stations 20. During the handover signaling, the first RNC 30, i.e RNC1 in FIG. 1, establishes the necessary connections Bxe2x80x2 via RNC2 to base stations 20 controlled by the RNC2, and releases the former connections Axe2x80x2 to the base stations 20 controlled by the RNC1. The controlling RNC, i.e., RNC1 in FIG. 1, is commonly called the controlling RNC. The other RNC, i.e., RNC2 in FIG. 1, is commonly called the drift RNC. Further, in some specifications for the UMTS (Universal Mobile Telecommunication System), the interface between two RNCs is called the Iur interface, and the interface between a MSC and RNC is called the Iu interface. These interface names are used in this specification.
The system of FIG. 1, namely the use of a controlling RNC and a drift RNC, has certain drawbacks which arise from the fact, that in situation B the transmission links are routed via two RNC:s, instead of only one as in situation A. As the number of transmission links increase, also the delays created by the links increase. The increase of delays places more demands on the whole network, when the network has to fulfill strict delay requirements for constant delay services, such as speech. Further, since the number of transmission links in use increases, the load on the network increases.
An object of the invention is to optimize transmission links in a cellular telecommunications network, when a mobile station has moved from an area controlled by a first radio network controller to a second area controlled by a second radio network controller. Another object of the invention is to realize a method for reducing transmission delays between the controlling radio network controller and the base stations in a situation, when a mobile station has moved from an area controlled by a first radio network controller to a second area controlled by a second radio network controller. A further object of the invention is to realize a method for reducing network load in a situation, when a mobile station has moved from an area controlled by a first radio network controller to a second area controlled by a second radio network controller. A still further object of the invention is to alleviate the aforementioned problems.
The objects are reached by relocating the connection controlling entities from the first radio network controller to the second radio network controller, whereby the second radio network controller becomes the controlling radio network controller, and by optimising the links between the mobile switching center being used and the second radio network controller.
The invention describes the realisation of transmission link optimisation in a situation, where a mobile station has moved from a network area controlled by a first radio network controller (RNC) RNC1 to a network area controlled by a second radio network controller RNC2. Signalling associated with the procedure is executed between the two RNCs and a mobile switching center (MSC). The mobile station does not need to participate in the signaling, since the used radio resources remain the same. The object of this procedure is to optimise the utilisation of transmission links in the radio access network (RAN) being used and to minimise the transmission delay between the controlling RNC and the radio interface. This is realised by relocating the entities which control connections of a mobile station from the first RNC to the second RNC, and optimizing the transmission links between the MSC and the second RNC. Such controlling entities may comprises, e.g., the macrodiversity combining function, radio resource control block and associated user plane entities.